Status of Coral Communities in American Samoa: A Re-survey of Long-term Monitoring Sites in 2002 (NODC Accession 0001470)

Abstract:

This data set consists of an MS Word file which documents and summarizes data previously submitted as MS Excel spreadsheets to the NOAA data centers, NODC ACCESSION 0000735. The present MS Word file contains some data not found in the spreadsheets and this final report shows the trends in terms of bar diagrams which is a quicker form of communication. A re-survey of coral communities in the American Samoa Archipelago covering the island of Tutuila and the Manu'a Group of islands (Ofu, Olosega, and Tau), was carried out during March 2002. All surveyed sites in 2002 were restricted to the 10m deep slope habitat only. The 1995 baseline survey utilized a larger sample size (belt width) within replicate transects, that could not be duplicated in the allocated time for the present survey due to the significant increase in colony densities. The same number of belt transects (5 per site) was used in both surveys for the Manu'a Group sites, but the number of transects per site was reduced to 3 per site on Tutuila. Consequently, sample unit size per site was 50% to 70% of the area sampled in 1995. Data were analysed to investigate changes in coral colony size structure, cover, and density, and to interpret community dynamics. The variation in sample effort between surveys and to a less extent, among sites in 2002, meant that pooled analyses were limited, so descriptive and statistical tools were used to interpret community dynamics during the period between the two surveys. Threats and disturbances were also interpreted from features of the coral community dynamics, which included the impacts (and current extent) of coral bleaching as well as crown of thorns starfish infestations.

Original file: AmSamoaFisk.doc, MS Word format.An ASCII copy was placed in ../../data/AmSamoafisk.txt.This is the complete technical/data report for thissurvey. Data are stored in tables within this document as follows.The same data are found in MS Excel spreadsheets withinNODC ACCESSION 0000735.Table 1. Summary of sites and methods employed in the present study compared to the initial baseline survey of Mundy (1996).Table 2. Methods used in the present survey (Fisk & Birkeland 2002) at Faga and Lepula (Tau Island, Manua Group) that varied from the standard replicate 20m x 0.25m belt transects..Table 3. Numbers of colonies per site that were recorded in both 1995 and 2002.Table 4. Summary of genera colony numbers recorded in the 2002 and 1995 surveys at comparable sites and habitats that were surveyed at both times.Table 5. Summary of the presence or absence of coral species on Tutuila and the Manua Group from the 2002 survey.Table 6. Summary of the presence or absence of coral species on Tutuila and the Manua Group from the 1995 survey.Table 7. Rank of top 10 most abundant species from the two surveys at Fagafue.Table 8. Rank of top 10 most abundant species from the two surveys at Fagasar.Table 9. Rank of top 10 most abundant species from the two surveys at Vatia.Table 10. Rank of top 10 most abundant species from the two surveys at Masefau.Table 11. Rank of top 10 most abundant species from the two surveys at Aunuu.Table 12. Rank of top 10 most abundant species from the two surveys at Fagaitua.Table 13. Rank of top 10 most abundant species from the two surveys at OnesosopoTable 14. Rank of top 10 most abundant species from the two surveys at Aua.Table 15. Rank of top 10 most abundant species from the two surveys at Fagaalu.Table 16. Rank of top 10 most abundant species from the two surveys at Fatumafuti.Table 17. Rank of top 10 most abundant species from the two surveys at Fagatele.Table 18. Rank of top 10 most abundant species from the two surveys at Leone.Table 19. Rank of the top 10 most abundant species from the two surveys at Asaga.Table 20. Rank of the top 10 most abundant species from the two surveys at Sili.Table 21. Rank of the top 10 most abundant species from the two surveys at Olosega Village.Table 22. Rank of the top 10 most abundant species from the 2002 survey at HurricaneTable 23. Rank of the top 10 most abundant species from the two surveys at Ofu Village.Table 24. Rank of the top 10 most abundant species from the two surveys at Faga.Table 25. Summary of top ten ranked species of non-Montipora spp at Faga.Table 27. Summary of top ten ranked species of non-Montipora spp at Lepula.Table 28. Rank of the top 10 most abundant species from the two surveys at Afuli.Table 29. Rank of the top 10 most abundant species from the two surveys at Fagamalo.Table 30. Summary of the degree of bleaching that was observed in March 2002.Table 31. Summary of trends described in detail for each monitoring site.Appendix 1. Raw data from the 2002 survey presented in size frequency categories.Original file: AGreen_transects.doc, MS Word formatRedundant copy placed in HTML format in directory html,which contains a directory of JPEG figures depicting stationlocations.Files Lat-Long.doc (MS Word) and redundant ASCII copy Lat-Long.txtprovide explicit coordinates of survey locations.

Dr. Charles Birkeland
U.S. Department of the Interior, U.S. Geological Survey, Hawaii Cooperative Fishery Research Center, University of Hawaii at Manoa
Marine Biologist
Edmonton 164, University of Hawaii at Manoa
Honolulu, Hawaii 96822
USA

The principle objective was to assess the status of coral communities and to provide detailed analysis of temporal change between the initial baseline coral survey of 1995 and the present survey of 2002. A second objective was to recommend areas for future consideration for inclusion into Marine National Parks.

The Department of Marine and Wildlife Resources conducts expert surveys of marine resources every 5 years on behalf of the American Samoa Government. These specialist surveys are part of a broad monitoring plan (Cornish and Wilson, 2002) for the Territory. and include quantitative assessments of coral, fish, crown of thorns starfish, and giant clams. The coral baseline monitoring sites were first established in October - November 1995 (Mundy 1996), and were conducted at the same time using the same transects that were used for fish, invertebrate and habitat surveys (Green 1996). In the initial baseline survey, Mundy (1996) concluded that the reefs throughout American Samoa were in a recovery phase following a combination of natural and anthropogenic disturbances, and that the communities were diverse and complex in structure. His conclusions were made from a survey of 29 sites spread throughout Tutuila Island and the Manu'a Island group, where the size, density and cover of corals were estimated. Quantitative surveys of hard corals were carried out during March 2002. Delays in organising the re-survey meant that there was an approximate 6.3 year interval between the two surveys. All sites from the 1995 survey were not resurveyed in 2002, nor were all habitats. In contrast to Mundy's (1996) survey, no reef flat or lagoon sites were surveyed in 2002. The current survey included a total of 21 sites made up from Tutuila Island (12 sites) and the Manu'a Islands (Ofu (3 sites), Olosega (2 sites), and Tau Islands (4 sites)). The site at Aunu'u Island off the SE corner of Tutuila Island is included in the Tutuila suite of sites as it is closely affiliated with this island. At all sites, surveys were conducted on the reef slope at approximately 10m depth and in the same general location as the previous surveys in 1995 (Mundy 1996). One new site was established on Ofu Island during the current survey to augment the extensive survey work that has been carried out in the adjacent Ofu lagoon marine park. At 11 sites on Tutuila, three replicate 20m belt transects, with a width of 0.25m, were surveyed for coral species size and density. At one site on Tutuila (Fagaitua), a 5m length of one transect was incompletely surveyed due to lack of time. In the Manu'a Group, six sites were re-surveyed using 5 replicate 20m belt transects, with a belt width of 0.25m. One site (Ofu Village) was re-surveyed using the same 0.5m width in 5 replicate 20m transects that were used in 1995, and two sites were surveyed on Tau using variable belt widths and lengths due to the rough conditions. The baseline survey in 1995 used five replicate belt transects with 20m length for each transect, but the belt width was 0.5m, which is double the present survey width used in most sites in 2002. Usually, two divers equally shared the coral survey effort at each site. It became apparent after we commenced the surveys, that colony densities were generally much higher than in 1995. We decided to halve the belt width and where necessary, to reduce the number of belt transects (on Tutuila mainly) to ensure we would complete sufficient sites in the allocated time, and sample sufficient colonies at each site to make meaningful comparisons. Coral communities at several sites were not re-surveyed in this study though they were surveyed in 1995. These included : (on Tutuila) Leloaloa slope, Utulei slope, Faga'alu lagoon, Fatumafuti reef flat, Nu'uuli slope, Nu'uuli reef flat, Amanave slope; (on Manu'a) Ofu Village reef flat and Olosega reef flat. Two sites (Faga and Lepula) on Tau Island (Manu'a Group) were not surveyed in the same way as the 1995 survey because of the very high density of colonies present, time constraints, and adverse sea conditions (Table 2). Two divers shared the survey effort, but not generally in an equal manner. As well, it was decided to survey some belt transects for all coral species and to survey additional belt transects for all non-Montipora spp colonies, as this genus was extremely abundant and frequently fragmented throughout the sites. Consequently, extra effort was allocated to the non-Montipora spp component of the community (at the expense of the Montipora spp component) to ensure that adequate sample numbers were obtained for colony density and size class analyses of this group. Table 2 shows the total area that was surveyed for the two sites of Faga and Lepula, and the areas surveyed for both non-Montipora spp and all species combined. Each transect was surveyed by choosing usually 20m sections of five 50m transects that were deployed close to the substratum and parallel to the reef edge. A coral was considered to be within the transect if its centre was within the belt width. All corals within the belt were identified to species where possible, and the maximum diameter measured and recorded on the field data sheets. Colony sizes (maximum diameter) were measured in situ to the nearest centimeter and data are presented in size categories. The same size categories that were used by Mundy (1996) were used here. These size class categories are : 1 = <=5cm, 2 = > 5 to <=10cm, 3 = >10 to <=20cm,4 = >20 to <=40cm,5 = >40 to <=80cm,6 = >80 to <=160cm, and 7 = >160cm. Colonies that were showing signs of bleaching were noted in the field at the same time as other information was recorded. Coral cover was estimated using the three point intercept sampling method which produced percent cover data from 75 points per transect. Five 50m transects were used to estimate cover at each site. Full details of the method and calculation of results are reported separately in Green (2002). Data Analysis The change in monitoring methods between the two surveys was unavoidable and necessary to complete an adequate number of sites in the alloated time. As well, the methods differed between surveys in the Manu'a Island Group and from Tutuila Island Group. The variation in sampling methods limited the type of statistical comparisons that could be employed between the two surveys and between the two major subset groups from Manu'a and Tutuila. Comparisons between surveys were predominantly descriptive and based on within-site analyses, though broader general trends were highlighted in the overall discussion. Within-site analyses and discussion focused on colony density, species richness, species change or turnover, and community structure (that is, dominant growth form and size class structure). It is recognised that analyses based on species presence/absence comparisons among sites and between the same sites over time are invalid when sampling effort varies. This is because rare or low abundant species are more likely to be recorded as sampling effort increases. Nonetheless, comparisons are made for each site using species richness (number of species) as a measure of diversity. The significance of species richness comparisons was only highlighted when the number of species recorded at a site in 2002 exceeded or approximately equalled that recorded in 1995 (which was surveyed with greater sampling effort). When species richness was much lower in 2002 than in 1995, no conclusions were made from these results. Most multivariate statistical analyses of data sets also assume that equal sample effort has been used so that presence/absence species lists represent a true comparative estimate of community composition among sites. As the sampling regime varied between sites from the Manu'a group and Tutuila, as well as within sites from these two major site groups, results would have been less significant if analyses concentrated on those sites that were sampled in the same manner. Species comparisons were only made for the top ten ranked species from each site and when the total number of colonies recorded in 2002 was similar to or greater than the colony numbers recorded in 1995. In the majority of sites, these two conditions were met. A low similarity between surveys in the top ranked species was defined when the top ten most abundant species had less than 4 species in common. A moderate similarity was defined when the top ten species lists from both surveys had four to six species in common. A high similarity between surveys was defined as both surveys having greater than six species in common.G-statistic analyses for goodness of fit based on the pooled size frequencies from both surveys were included when the total number of sampled colonies was approximately equal in both survey times, and when other assumptions and restrictions on the use of the G-statistic were satisfied. It was assumed that survey times and the placement of belt transects from each survey were random and that the resultant data were representative of that site. The G statistic is generated from the log-likelihood ratio, which approximates the chi-square distribution when expressed as twice this quantity (referred to as the G statistic, Zar 1984). It is recommended that assumptions pertaining to the chi square be adhered to for the G test (Zar 1984). These include : no expected frequency be less than 1%, and more than 20% of all expected frequencies are greater than 5. When these conditions are not present, it is recommended that the low frequency categories be eliminated from analyses or that adjecent categories with low frequencies are combined. When a few categories could be pooled to satisfy the G-test assumptions this was carried out prior to analyses. For species where size categories had too few observations such that pooling categories would not satisfy the above conditions, analyses were not carried out. Chi square tables were consulted after the G statistic was calculated, with the degrees of freedom equalling the number of size categories used to calculate the G-statistic minus 1. The null hypothesis was that the size class frequencies are the same for both survey times. The alternative hypothesis was that size class frequencies are not the same for both survey times.

Person who carried out this activity:

Dr. Charles Birkeland
U.S. Department of the Interior, U.S. Geological Survey, Hawaii Cooperative Fishery Research Center, University of Hawaii at Manoa
Marine Biologist
Edmonton 164, University of Hawaii at Manoa
Honolulu, Hawaii 96822
USA

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